There is known a method of manufacturing a foamed or porous metal by adding a foaming agent to a molten or powdered metal and gasifying the foaming agent under heat or otherwise to form numerous pores in the metal (see, for example, Japanese Patent No. 2,898,437). In the narrow senses of the words, a foamed metal containing gas in its pores differs from one not containing such gas, but since they are equal in having numerous pores, they are herein referred to together as a foamed or porous metal.
Japanese Patent No. 2,898,437 gives 0.2% by weight of titanium hydride and sodium hydrogen carbonate as specific examples of a foaming agent. The use of titanium hydride or sodium hydrogen carbonate having a high reducing power is usual for foaming aluminum having a high affinity for oxygen. Titanium hydride and sodium hydrogen carbonate, however, have the draw-back that they are expensive and raise the cost of manufacturing a foamed or porous metal. Moreover, they produce hydrogen gas which is so explosive as to call for the utmost care in handling and thereby impose a heavy burden on the workers. Thus, there is a serious demand for a foaming agent which can be used at a low cost without producing any danger of hydrogen explosion when manufacturing a foamed or porous metal.